The distance "d" that it has fallen is proportional to the square of the time "t" since you dropped it:
for some constant "k".
The questions asks: If you dropped a rock and it fell 4.9m in 1s, how far would it fall in 3s?
Changing "x" by a factor of 'c' changes "y" by a factor of c^2.

For example:

So:
d = 4.9 * (3)^2
d = 44.1m
Your final answer is: 44.1m